Method and apparatus for solid-stranding a flextube unit

ABSTRACT

A solid-stranding method and apparatus for forming optical cables. Solid-stranding combines buffering and stranding operations, as well as performs the stranding operation while the flextubes are still hot so that they adhere together without additional binders. Optical fibers and/or wires are supplied to an extruder which forms flextubes around individual ones or groups of the optical fibers and/or wires. A central element may be supplied to, and go through, the center of the extruder. A rotating pulling device, such as a caterpillar, helically or in an SZ-manner solid-strands the flextubes around the central element—or solid-strands the flextubes to themselves when no central element is present—as the flextubes cool down. That is, solid-stranding includes buffering and stranding operations that are performed together without a water cooling stage therebetween. Thus, the flextubes adhere together, and may adhere to the central member, thereby forming a solid-stranded composite core. The solid-stranded composite core then may be jacketed by passing through another extruder, or may be used without a jacket, thereby forming a solid-stranded flextube unit from which individual flextubes easily may be split.

BACKGROUND

[0001] 1. Field of the Invention

[0002] The present invention is directed to a method and apparatus formanufacturing optical cables and, in particular, optical cables whichinclude flextubes having optical-fibers therein.

[0003] With the advent of local area networks and the relative broadbandcapabilities of fiber optic links, it has become commonplace for newcommunication systems to include fiber-optic capabilities. Communicationcables employing optical fibers—optical cables—are widely used in thetelecommunications industry. In particular, multifiber optical cablesare widely used for long distance telephone communications,interexchange telephone applications, and other telephony and datatransmission applications. Optical cables are also being incorporatedinto cable television networks in place of more traditional coaxialcables. Optical cables may permit long distances between signalrepeaters or eliminate the need for such repeaters altogether. Inaddition, optical fibers offer extremely wide bandwidths and low noiseoperation.

[0004] 2. Related Art

[0005] In the use of optical fibers, optical cables are provided forphysical protection of the fibers in view of the fragile nature of theglass optical fibers. An optical cable may contain many optical fiberswhich must be identified and manipulated without disturbing otheroptical fibers within the optical cable. Therefore, optical cables mayhave various internal structures. The structure families which arecurrently being used are tight tube, monotube, slotted core, and loosetube.

[0006] In the tight buffer tube construction, protective layers areapplied in direct contact with each optical fiber so there is no fiberoverlength. In such a tight buffered construction, each optical fiberhas one or more completely encapsulating layers in order to providemechanical protection. The protective layers may be made ofthermoplastic or other suitable materials. The protective layerstypically have material properties which give the buffered fiber goodmechanical and thermal performance. The value of cable tensileelongation for the buffered fiber is typically less than 0.15% in orderto provide low attenuation increase at low temperatures.

[0007] In the monotube structure, all of the optical fibers are housedin a single, centrally located, gel filled, oversized, thermoplastic,buffer tube. The optical fibers may be loosely configured, grouped inbundles wrapped by binders, or held in a matrix by ribbons. The hollowbuffer tube is typically filled with a thixotropic gel which blockswater penetration, but allows for fiber movement during cable expansionor contraction. A precise amount of fiber overlength within the buffertube is required in order for the fibers to maintain a virtualstress-free condition during cable expansion. The amount of overlengthis typically within 0.1-0.2% of the value for the amount of cabletensile elongation.

[0008] The slotted core structure has optical fibers precisely placed ingel filled channels or slots. The channels are symmetrical and form ahelical path along the longitudinal axis of the cable. A strength memberis located in the center of the slotted core cable structure. That is,in the slotted core construction of optical cable, a profile member isextruded around a central strength member made of metallic or dielectricmaterial. A plurality of slots or grooves which follow a helical orreversing helical path are located on the outer surface of thethermoplastic profile member. One or more optical fibers lay in theslots in a virtual stress-free condition. The optical fibers may beloosely configured, grouped in bundles wrapped with binders, or held ina ribbon matrix.

[0009] Finally, in a loose tube or flextube structure, several buffertubes containing optical fibers are stranded around a central strengthmember. The buffer tubes are then typically bound together with aseparate binder before being enclosed within a common sheath. Withrespect to identifying and manipulating the optical fibers withoutdisturbing or damaging other optical fibers within a cable, the loosetube or flextube structure offers advantages over the monotube. A singlebuffer tube may be accessed in the loose tube or flextube structurewhile the remainder of fibers within other buffer tubes are undisturbed.In contrast, entry into the single central monotube is likely toincrease the risk of damaging adjacent fibers because all of the fibersare contained within the single monotube.

[0010] Loose tubes include extruded cylindrical tubes—called buffertubes—which enclose optical fibers in a cable. The optical fibersenclosed within a loose tube may be in the form of single opticalfibers, optical-fiber ribbons, or any other configuration of opticalfibers, which are simply referred to hereinafter as optical fibers forconvenience. The buffer tubes serve many purposes, for example:providing physical protection to the optical fibers; protecting theoptical fibers from contaminants; containing water blocking materials;isolation of the optical fibers into groups; strengthening the cable toresist crushing forces; and providing room for optical fibers to movewhen the cable is bent and when tension is applied to the cable.

[0011] In conventional methods, individual loose tubes are first formed,as in a buffering process, and they are then stored as an intermediateproduct, for example on a plate or drum. A plurality of these loosetubes are then stranded together—in a separate stranding process whichoften takes place in a different location—to form an optical-fibercable, or loose tube unit. An example of this type of method isdisclosed in U.S. Pat. Nos. 5,938,987 and 4,171,609, wherein the formerdiscloses a method by which individual loose tubes are formed, i.e., abuffering step, and the latter discloses a method by which individualpreformed loose tubes are stranded together, i.e., a separate strandingstep. However, winding the loose tubes onto a drum or depositing theloose tubes represents additional work outlay and cost. Further cost isassociated with storage and transportation of the individual loose tubesto the stranding location.

[0012] U.S. Pat. No. 5,283,014 attempts to solve the problems of usingseparate process lines and/or locations to first form individual loosetubes (buffering) and then strand them together. This patentconsecutively disposes buffering and stranding lines so that individualloose tubes are formed, are cooled so as to solidify, and are thenstranded together along one process line, thereby avoiding storage andtransportation costs involved in other conventional methods. However,the buffering and stranding processes are still separate and, therefore,this process still suffers drawbacks associated with separate bufferingand stranding processes, such as high cooling costs and low line speedsas it completely cools the loose tubes before it strands them together.Further, the loose tubes are bound together with a separate binderbefore being enclosed within a common sheath, thereby adding processtime as well as expense.

[0013] Flextubes are similar to loose tubes in that they contain asupporting sheath which surrounds optical fibers in a cable. The opticalfibers enclosed within a flextube may be in the form of single opticalfibers, optical-fiber ribbons, or any other configuration of opticalfibers, simply referred to hereinafter as optical fibers forconvenience. The supporting sheaths of flextubes serve many purposes,for example: providing physical protection to the optical fibers;protecting the optical fibers from contaminants; containing waterblocking materials; isolation of the optical fibers into groups; andstrengthening the cable to resist crushing forces.

[0014] Although flextubes are similar to loose tubes, they have severaldifferences. In particular, flextubes for a given number of opticalfibers have an outside diameter which is smaller than that for a loosetube having the same number of optical fibers. In other words, thesupporting sheath of a flextube lies more tightly around the opticalfibers than does a buffer tube of a loose tube. That is, the supportingsheath is disposed in contact with the optical fibers so as to surroundthem in such a manner as to achieve mechanical coupling between theoptical fibers. Alternatively, there may be a very small space betweenthe supporting sheath and some of the optical fibers therein. Further,the supporting sheath is more flexible than a buffer tube, and is notnecessarily cylindrical as is a buffer tube. That is, the supportingsheath conforms to the optical fibers which it surrounds, whereas abuffer tube is a rigid cylinder having the optical fibers therein.Because of the manner in which flextubes are formed, they are lighter inweight and smaller in size than their loose tube counterparts. Further,because the supporting sheaths are more flexible than buffer tubes, itis easier to access—without special tools—the optical fibers within aflextube than it is to access the optical fibers within a loose tube.That is, the supporting sheaths may be easily removed with bare fingersor by simple tube access tools.

[0015] Despite the differences between flextubes and loose tubes,flextubes are formed into optical-fiber cables in a similar manner asdescribed above for loose tubes. Accordingly, the heretofore methods ofproducing flextubes into flextube units or optical cables suffer thesame disadvantages noted above for the production of loose tubes intooptical cables.

SUMMARY OF THE INVENTION

[0016] An object of the present invention is to overcome thedisadvantages of the related art. In particular, it is an object of thepresent invention to increase line speed and decrease cost in theproduction and use of flextube units, or optical cables.

[0017] The present invention achieves the above and other objects andadvantages by providing a new process, in manufacturing optical cables,called solid-stranding. The process of solid-stranding is a one-stepprocess for extruding multiple loose tubes or flextubes (hereinaftersimply referred to as flextubes for convenience) and stranding the tubesin helical or SZ stranded arrangement prior to winding the optical cableon a take-up reel. The method and apparatus of the present invention,for solid-stranding, combine together buffering and strandingoperations, as well as perform the stranding operation while thesupporting sheaths of the flextubes are still hot so that they adheretogether without additional binders. In particular, optical fibersand/or wires are supplied to an extruder which forms supporting sheathsaround individual ones or groups of the optical fibers and/or wires. Acentral element is supplied through the center of the extruder. Arotating pulling device, such as a caterpillar, helically strands theflextubes around the central element as the sheaths cool down. That is,in the new solid-stranding process of the present invention, bufferingand stranding operations are performed together without a cooling stagetherebetween so that the flextubes contact one another and the centralelement at a temperature which is between the process temperature andthe melting point of the material from which the flextubes are made. Theprocess temperature is that of the material in the extruding die and,typically, is 20-50° C. above that material's melting point, wherein themelting point is typically a range of temperatures over which thematerial melts. Although the melting point is actually a range oftemperatures over which the material melts, the term “melting point” isused for convenience. Thus, because the flextubes are brought togetherat a temperature which is between the process temperature and themelting point, they adhere together forming a composite core. Thecomposite core then may be jacketed by passing through another extruder,or may be used without a jacket, thereby forming a flextube unit fromwhich individual flextubes easily may be split.

[0018] Because there is no need to completely cool the flextubes beforethey are stranded, and the flextubes have a relatively thin supportingsheath wall, water cooling of individual flextubes can be replaced byair cooling the composite core. That is, cooling water right afterextrusion becomes unnecessary. Therefore, any water swellable elementsused in the flextube unit are not damaged. Additionally, air cooling—asopposed to water cooling—the flextubes may help to improve thebreakability and split of the supporting sheath, when it is desired todo so. That is, water cooling may undesirably change the mechanicalbehavior of some polymers, like those based on polypropylene (PP). Suchundesirable change in mechanical behavior is eliminated by air coolingthe flextubes after they have been stranded together.

[0019] Further, solid-stranding—wherein buffering and stranding areperformed in the same process—shortens manufacturing time. That is,skipping the cooling stage—wherein individual flextubes are formed,which must then be combined in a stranding phase—increases productionspeed.

[0020] Moreover, solid-stranding forms a composite core which eliminatesthe need for separate binders to hold the flextubes together.Conventional cable designs produced by separate buffering and strandingprocesses may use a minimum of one binder—typically a polyester yarn—tosecure all the loose tubes or flextubes during the tube stranding step.The binder allows the tubes to remain at desirable locations, such as inhelically or SZ-stranded arrangements. However, the binders add costs inmanufacturing material and equipment, as well as labor burden in thefield to remove the binder prior to accessing the tubes. Becauseseparate binders are not necessary in the solid-stranding process of thepresent invention, production speed is further increased and, at thesame time, production cost is reduced. Further, such results in a lowercost optical cable, the tubes and optical fibers of which can be moreeasily accessed in the field thereby reducing labor costs involved withuse and repair of the optical cable.

[0021] The solid-stranded flextubes may be continuously helicallystranded in one direction, or may change stranding directions to form anSZ-stranded composite core. Further, the central element may be a waterswellable yarn, a ripcord, or itself may be a flextube having opticalfibers therein. Alternatively, the central element may be a metallic orother heat conducting member. In this case, the central element can beheated to further promote adhesion between the flextubes stranded aroundit, as well as to assist in sticking the flextubes to the centralmember.

[0022] Although a single central element is described above, such is notnecessary. Instead, a plurality of flextubes may be stranded togetherwithout a central element. Further, the flextubes may be strandedtogether with water blocking elements such as yarns or powders. Theflextube unit may then be wrapped in a water blocking tape, surroundedby armoring, and then encased in a sheath having strength memberstherein.

[0023] The individual flextubes which make up the solid-strandedflextube unit have sheaths made of conventional materials such as, forexample, plastic material including polyethylene (PE), polybutyleneterephthalate (PBT), polypropylene (PP), polyvinyl chloride (PVC),polyamide (PA), and/or ethylene vinyl acetate (EVA), as well ascopolymers and/or blends of the above materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects and advantages of the presentinvention will become more apparent by describing in detail preferredembodiments thereof with reference to the accompanying drawings, whereinlike reference numerals designate like or corresponding parts throughoutthe several views, and wherein:

[0025]FIG. 1 is a schematic side view of an apparatus for implementingthe solid-stranding method of the present invention;

[0026]FIG. 2 is an end view of an extruder head for employment in thesolid-stranding method of the present invention;

[0027]FIG. 3 is an enlarged transverse cross sectional view of thestructure of two adjacent solid-stranded flextubes that are formed bythe extruder head of FIG. 2;

[0028]FIG. 4 is a schematic transverse cross sectional view of asolid-stranded flextube unit as produced by the method and apparatus ofthe present invention;

[0029]FIG. 5 is a schematic transverse cross sectional view of asolid-stranded flextube unit having a jacket around it, according to thepresent invention;

[0030]FIG. 6 is a schematic transverse cross sectional view of anarmored, solid-stranded, flextube cable according to the presentinvention; and

[0031]FIG. 7 is a schematic transverse cross sectional view of anotherembodiment of a solid-stranded flextube cable according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The method and apparatus of the present invention are directed toa new and novel solid-stranding process. The solid-stranding process ofthe present invention combines buffering and stranding operations, aswell as performs stranding while the flextubes 13 ₁-13 _(n) are stillhot so that they adhere together without additional binders, therebyproducing a solid-stranded flextube unit. The flextubes 13 ₁-13 _(n) areformed by optical fibers 12 ₁-12 _(n) that are supplied to an extruder20, and supporting sheaths (also called flextube walls) 16 ₁-16 _(n)formed by the extruder 20 around individual ones or groups of theoptical fibers 12 ₁-12 _(n). A central element 14 is supplied throughthe center of the extruder's head 21. A rotating pulling device, such asa caterpillar 30, helically strands the flextubes 13 ₁-13 _(n) aroundthe central element 14 as the flextubes 13 ₁-13 _(n) cool down. That is,in the solid-stranding process of the present invention, buffering andstranding operations are performed together without a cooling stagetherebetween so that the flextubes 13 ₁-13 _(n) are brought togetherwhile their walls 16 ₁-16 _(n) are at a temperature which is between theprocess temperature and the melting point of the material from whichthey are made. The process temperature is that of the material in theextruding die and, typically, is 20-50° C. higher than the meltingpoint, wherein the melting point is a range of temperatures over whichthe material melts. Thus, because the flextubes 13 ₁-13 _(n) are broughttogether wherein their walls 16 ₁-16 _(n) are at a temperature betweenthe process temperature and the melting point, they adhere to oneanother, as well as to the central element, thereby forming asolid-stranded flextube unit 1, wherein the flextube walls 16 ₁-16 _(n)form a composite core of the flextube unit 1. The solid-strandedflextube unit 1 may then be jacketed by passing it through anotherextruder, or may be used without a jacket, thereby forming asolid-stranded flextube unit from which individual flextubes 13 ₁-13_(n) easily may be split.

[0033] The method and apparatus for forming a solid-stranded flextubeunit 1 will be described with reference to FIGS. 1 and 2. The apparatusincludes a supply drum 4 having a central element 14 thereon, supplydrums 2 ₁-2 _(n) having optical fibers 12 ₁-12 _(n) thereon, an extruder20 having an extruder head 21 with nozzles 23 ₁-23 _(n), and a rotatingcaterpillar 30.

[0034] The supply drum 4 and the supply drums 2 ₁-2 _(n) provide thecentral element 14 and the optical fibers 12 ₁-12 _(n), respectively, tothe extruder head 21. For convenience in explanation, and clarity ofillustration, only one supply drum and one optical fiber are shown foreach flextube. However, any suitable number of optical fibers may beused within one flextube and, therefore, a corresponding number ofsupply drums may be used to provide that number of optical fibers to thedesired nozzle in the extruder head 21. Alternatively, a group ofoptical fibers may be supplied on a single supply drum for conveyance toa single nozzle. That is, although only one supply drum and one opticalfiber per nozzle opening are shown for clarity of illustration, theremay be more than one supply drum per nozzle opening, and each supplydrum may contain a single optical fiber, a plurality of loose or boundoptical fibers, a ribbon of optical fibers, a stack of ribbons, or anyother suitable configuration of optical fibers.

[0035] The central element may be, for example, a central strengthmember made of metallic wires, plastic or glass-reinforced plastic rodsor, glass yarns or rods, or any other suitably strong material that istensile-load-resistant and compression-resistant so as to protect thesolid-stranded flextube unit 1 from tensile and compressive loads.Further, when the central element conducts heat, it may be heated as theflextubes are twisted therearound to promote better adhesion between thecentral element and the flextubes. Alternatively, the central elementmay be omitted or may be replaced by another flextube—or group offlextubes—having optical fibers therein.

[0036] The extruder head includes a central bore 24 to receive thecentral element 14, and also includes nozzles 23 ₁-23 _(n) to formflextube walls 16 ₁-16 _(n) around the optical fibers 12 ₁-12 _(n),thereby forming flextubes 13 ₁-13 _(n). Alternatively, when it isdesired to have a central element that is a flextube—or group offlextubes—the bore 24 is also a nozzle, or nozzles, similar to nozzles23 ₁-23 _(n). The nozzles 23 ₁-23 _(n) are arranged concentricallyaround the central bore 24. Although only six nozzles 23 ₁-23 ₆ areshown, any number of nozzles may be present depending on the desirednumber of flextubes 13 ₁-13 _(n) to be included in the solid-strandedflextube unit 1. Further, the nozzles 23 ₁-23 _(n) extend through theextruder head 21 so as to guide the optical fibers 12 ₁-12 _(n) as theflextube walls 16 ₁-16 _(n) are formed around them to produce theflextubes 13 ₁-13 _(n). The nozzles 23 ₁-23 _(n) enable the entry of atleast one optical fiber, 12 ₁ for example, that is hauled off from acorresponding supply drum 2 ₁. Of course, it is also possible to draw aplurality of optical fibers, ribbons, conductors, or cords through acorresponding nozzle. When a total of n flextubes is desired to bemanufactured for a solid-stranded flextube unit 1, for example, acorresponding number of supply drums 2 ₁-2 _(n) may be provided inaccordance with the schematic illustration of FIG. 1. Alternatively,each of the supply drums 2 ₁-2 _(n) may, in fact, be a plurality ofsupply drums so that any suitable number and configuration of opticalfibers may be conveyed to each of the nozzles 23 ₁-23 _(n). Further, itis not necessary for all the supply drums 2 ₁-2 _(n) to be of the sameconfiguration. That is, for example, supply drum 2 ₁ may include aplurality of supply drums, whereas supply drum 2 ₂ may only include onesupply drum.

[0037] A hose-shaped flextube wall is produced by the extruder head 21in the region of discharge from each of the nozzles 23 ₁-23 _(n). Theseflextube walls 16 ₁-16 _(n) contain at least one optical fiber 12 ₁-12_(n) on their inside so that the overall arrangement forms a group ofsolid-stranded flextubes 13 ₁-13 _(n). The flextube walls 16 ₁-16 _(n)may be made of conventional materials such as, for example, plasticmaterial including polyethylene (PE), polybutylene terephthalate (PBT),polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), and/orethylene vinyl acetate (EVA), as well as copolymers and/or blends of theabove materials.

[0038]FIG. 3 shows two adjacent flextubes 13 ₁ and 13 ₂ just after theyhave exited the extruder head 21 and have been brought together. Justafter it has exited the extruder 20, the flextube 13 ₁ includes aflextube wall 16 ₁ and a plurality of optical fibers 12 ₁ therein. Theflextube walls 16 ₁ and 16 ₂ respectively surround the optical fibers 12₁ and 12 ₂ in such a manner as to achieve mechanical coupling betweenthe optical fibers. The is, the flextube wall 16 ₁ surrounds a pluralityof optical fibers 12 ₁ so as to form a mechanical coupling between theplurality of optical fibers 12 ₁ within the flextube 13 ₁. Similarly,the flextube wall 16 ₂ surrounds a plurality of optical fibers 12 ₂ soas to form a mechanical coupling between the plurality of optical fibers12 ₂ within the flextube 13 ₂. It should be noted that FIG. 3 is drawnon a greatly enlarged scale and, therefore, what appears as a relativelylarge space 5 between the optical fibers 12 ₁ in flextube 1 ₃₁, orbetween the optical fibers 12 ₂ in flextube 13 ₂, is in fact a space ofvery small size, or no space at all. Further, the flextube wall 16 ₁ isintended to keep the optical fibers 12 ₁ in close relation with oneanother so as to provide mechanical coupling between them, yet is thinenough that it easily may be torn by bare fingers to access opticalfibers in the field, other simple tube access tool may also be used.Although only three optical fibers 12 ₁ are shown within the flextube 13₁, any number of optical fibers may be included, and they may be in anydesired configuration such as, for example, a ribbon, or loose opticalfibers. Further, in addition to, or instead of, optical fibers, one ormore of the flextubes 13 ₁-13 _(n) may contain electrical wires, otherconductors, or cords. Although only two flextubes 13 ₁ and 13 ₂ areshown in detail, the structure of the remaining flextubes 13 ₃-13 _(n)is similar and, therefore, has been omitted for the sake of clarity ofillustration. However, although the structure of the flextubes 13 ₁-13_(n) is similar, they may contain different numbers of optical fibers,ribbons, conductors, or cords. That is, each of the flextubes 13 ₁-13_(n) does not need to include the same internal structure.

[0039] After the flextubes 13 ₁-13 _(n) exit the extruder head 21, theyare brought increasingly closer together until they lie on the outsidesurface of the central element 14. For the purpose of simplifying theillustration, the flextubes 13 ₁-13 _(n) are shown at a greater distancefrom the central element 14 in FIG. 1, while in reality they at leastone contacts at least a portion of the central element 14—as shown inFIGS. 4 and 5—at least in the region of the right-hand end of FIG. 1.

[0040] The rotating caterpillar, or other pulling device, 30 pulls theflextubes 13 ₁-13 _(n) from the extruder head, and twists them as itpulls. The rotating caterpillar 30 turns in the direction of the arrowshown in FIG. 1 to helically twist the flextubes 13 ₁-13 _(n) into asolid-stranded flextube unit 1. Alternatively, the rotating caterpillarcould change directions of rotation to provide an SZ-stranded flextubeunit. Further, the flextube walls 16 ₁-16 _(n) are not completely cooledbefore they are twisted together and, therefore, they stick to oneanother as well as to at least portions of the central element 14,thereby forming a solid-stranded flextube unit 1. That is, the flextubes13 ₁-13 _(n) are brought together when they are still hot and soft, sothat they stick to one another as well as to the central element 14. Butbecause the flextube walls 16 ₁-16 _(n) are thin, they air cool afterthe flextubes 13 ₁-13 _(n) have been twisted together. The rotatingcaterpillar 30 is positioned at a distance from the extruder head sothat the flextube walls 16 ₁-16 _(n) sufficiently air cool between thetime they are brought together to lie on the central element, and thetime they enter the caterpillar 30. Additionally, the extruder 20 andcaterpillar 30 are configured, and are positioned relative to oneanother, so that the flextube walls 16 ₁-16 _(n) adhere to one another,as well as adhere to the central member 14, as they are twisted by thecaterpillar 30. That is, the flextube walls 16 ₁-16 _(n) are notcompletely cooled between the time they exit the extruder 20 and thetime they are brought into contact with the central member 14. By way offurther explanation, as discussed above, the flextubes 13 ₁-13 _(n) arebrought into contact with one another, and with the central element 14,when their walls 16 ₁-16 _(n) are at a temperature which is between theprocess temperature and the melting point of the material from which thewalls 16 ₁-16 _(n) are made so that the walls 16 ₁-16 _(n) adhere to oneanother without binders.

[0041] By buffering and stranding the flextubes 13 ₁-13 _(n) in theabove manner, i.e., solid-stranding the flextubes 13 ₁-13 _(n), coolingwater becomes unnecessary right after extrusion because the heat is usedto adhere the flextubes 13 ₁-13 _(n) to one another as well as to atleast portions of the central element 14. By eliminating the necessityfor cooling water, the risk of damaging any water swellable elements issignificantly reduced in the solid-stranding process of the presentinvention.

[0042] A schematic cross-section of the solid-stranded flextube unit 1,after the flextubes 13 ₁-13 ₆ have been brought together so as to lie onat least portions of the central element 14, is shown in FIG. 4.Although the flextubes 13 ₁-13 ₆ are shown as circular in cross section,they have, in reality, flextube walls 16 ₁-16 ₆ more like the shapeshown in the greatly enlarged view of FIG. 3. This cross-section is thesame after the solid-stranded flextube unit 1 exits the caterpillar 30and is wound on a take-up reel (not shown). The solid-stranded flextubeunit 1 can be used in this configuration and, when so used, provides aflextube unit from which individual flextubes 13 ₁-13 ₆ easily may besplit for making connections, and the like. Further, for example, it maybe desirable to use some of the flextubes for long haul applications,and others of the flextubes for shorter distance connections. Therefore,this configuration easily can be used in the situation where flextubesfor shorter distance connections must be split away for splicing andbranching, whereas the ones used for long haul applications continuethrough branching locations to flextube unit terminals. Thus, a portionof the solid-stranded flextube unit easily may be diverted into a localarea, for example.

[0043] Alternatively, after the solid-stranded flextube unit 1 exits thecaterpillar 30—and before it is stored on a take-up reel—it may beconveyed through another extruder (not shown) which applies a jacket 18thereto. See FIG. 5. Again, in the schematic cross section of FIG. 5,although the flextubes 13 ₁-13 ₆ are shown as circular in cross section,they have, in reality, flextube walls 16 ₁-16 ₆ more like the shapeshown in the greatly enlarged view of FIG. 3. In this configuration, thesolid-stranded flextube unit 1 is stronger, and thus more suitable whenthe central element is not included or is replaced by a flextube, forexample. Further, in this configuration, a water blocking material, suchas a known type of water swellable yarn, a rip cord, or any other membermay be provided within the jacket 18 and in the interstices betweenflextubes 13 ₁-13 _(n). However, the flextubes 13 ₁-13 _(n) are not aseasily removed from the solid-stranded flextube unit when it is desiredto do so.

[0044] Alternative embodiments of an optical cable including asolid-stranded flextube unit as made according to the method of thepresent invention are shown schematically in cross section in FIGS. 6and 7. Again, in the schematic cross sectional views of FIGS. 6 and 7,although the flextubes 13 ₁-13 ₆ are shown as circular in cross section,they have, in reality, flextube walls 16 ₁-16 ₆ more like the shapeshown in the greatly enlarged view of FIG. 3. Also, the spaces, orinterstices, between the solid-stranded flextubes are exaggerated forclarity.

[0045] The optical cable shown in FIG. 6 includes a solid-strandedflextube unit 1′ made of eight flextubes 13 ₁-13 ₈, each having aplurality of optical fibers 12 ₁-12 ₈. That is, each flextube may haveone or more optical fibers therein. Flextubes 13 ₁-13 ₇ surround acentral flextube 13 ₈, which replaces the central element 14 of theprevious embodiments. The flextubes 13 ₁-13 ₈, form intersticestherebetween, and are held together without binders due to their wallsadhering to one another. Further, water blocking elements 41, such asyarns or powders, are included within the interstices of the flextubes13 ₁-13 ₈. The solid-stranded flextube unit 1′ is then surrounded by awater blocking tape 40, armoring 17, and a sheath 18′. The sheath 18′has strength members 19 therein. The strength members 19 may be, forexample, steel wires. Moreover, the sheath 18′ and the strength members19 may be made of any materials conventionally used for such purposes.

[0046] The optical cable shown in FIG. 7 includes a solid-strandedflextube unit 1″ made of eighteen flextube units 13 ₁-13 ₁₈, each havinga plurality of optical fibers 12 ₁-12 ₈ within a flextube wall as 16 ₁₈,for example, wherein no single central element is present. Instead, theflextube units 13 ₁-13 ₁₈ are bundled and twisted together so as to forminterstices therebetween, wherein the walls of the flextubes adhere toone another without binders. Again, each flextube may have one or moreoptical fibers therein, and the interstices are shown in an exaggeratedmanner for clarity. Further, water blocking elements 41′, such as yarnsor powders, are positioned in the interstices between the flextubes 13₁-13 ₆, and are bundled and twisted together therewith. Thesolid-stranded flextube unit 1″ is then surrounded by a water blockingtape 40′, and a sheath 18″ having strength members 19′ therein. Thesheath 18″ and the strength members 19′ may be made of any conventionalmaterials used for such purposes. Further, the optical cable shown inFIG. 7 includes ripcords 42 beneath, or in, the water blocking tape 40′layer to facilitate access to the flextubes 13 ₁-13 ₁₈.

[0047] It is contemplated that numerous modifications may be made to themethod and apparatus for solid-stranding a flextube unit of the presentinvention without departing from the spirit and scope of the inventionas defined in the following claims.

I claim:
 1. A solid-stranding method for making a flextube unitcomprising: forming a plurality of flextubes with an extruder, whereinthe flextubes include walls that are not completely cooled as they exitthe extruder; and twisting said flextubes together, while they are notcompletely cooled, so that said at least two of said flextube wallsadhere to each other upon cooling.
 2. The solid-stranding methodaccording to claim 1, wherein no water cooling is performed between saidflextube forming step and said flextube twisting step.
 3. Thesolid-stranding method according to claim 1, wherein said step oftwisting includes continuously twisting in one direction so as toprovide a helically stranded flextube unit.
 4. The solid-strandingmethod according to claim 1, wherein said step of twisting includestwisting in one rotational direction followed by twisting in an oppositerotational direction to provide an SZ-stranded flextube unit.
 5. Thesolid-stranding method according to claim 1, further comprising:providing a central element to said extruder so that said flextubes areformed concentrically around said central element.
 6. Thesolid-stranding method according to claim 5, wherein said step oftwisting includes twisting said flextubes so that said flextube wallslie on said central element when said flextube walls are not completelycooled and, thereby, adhere to said central element.
 7. Thesolid-stranding method according to claim 5, further comprising a stepof heating said central element.
 8. The solid-stranding method accordingto claim 1, further comprising forming a first one of said plurality offlextubes with a central portion of said extruder and forming theremaining ones of said plurality of flextubes concentrically around saidfirst one of said plurality of flextubes, and providing a jacket aroundsaid plurality of flextubes.
 9. The solid-stranding method according toclaim 1, wherein said step of twisting is performed with said flextubewalls at a temperature between a process temperature and a melting pointfor a material from which they are made.
 10. A solid-stranding methodfor making a flextube unit comprising: supplying at least two opticalfibers along separate paths to an extruder; utilizing said extruder toextrude a flextube wall around each of said at least two optical fiberssupplied to said extruder to thereby form at least two independentflextubes leaving the extruder, wherein the flextube walls are notcompletely cooled as they exit the extruder; stranding said at least twoflextubes together, while the flextube walls are at a temperature whichis between a process temperature and a melting point for a material fromwhich the flextube walls are made, so that said flextube walls adhere toone another.
 11. An apparatus for forming a solid-stranded flextube unitcomprising: an extruder having a plurality of nozzles for formingflextube walls; a rotating and pulling device disposed adjacent to saidextruder so as to entrain and twist flextubes produced by said extruder,wherein said extruder and said rotating and pulling device areconfigured, and are positioned relative to one another, so that saidflextube walls adhere to one another as they are twisted by saidrotating and pulling device.
 12. The apparatus according to claim 11,wherein said extruder includes a central bore, and said nozzles aredisposed concentrically around said central bore.
 13. The apparatusaccording to claim 12, wherein said extruder and said rotating andpulling device are configured, and positioned relative to one another,so that flextube walls produced by said extruder adhere to a centralelement fed through said central bore as said flextube walls are twistedaround said central element by said rotating and pulling device.
 14. Anoptical cable comprising: a solid-stranded flextube unit having aplurality of flextubes with interstices therebetween, each of saidplurality of flextubes having a flextube wall, wherein at least two ofsaid flextube walls are adhered to one another without a binder.
 15. Theoptical cable according to claim 14, further comprising a sheathsurrounding said solid-stranded flextube unit.
 16. The optical cableaccording to claim 15, further comprising at least one water blockingelement in at least one of said interstices.
 17. The optical cableaccording to claim 15, further comprising a water blocking tape betweensaid plurality of flextubes and said sheath.
 18. The optical cableaccording to claim 15, further comprising an armoring between saidplurality of flextubes and said sheath.
 19. The optical cable accordingto claim 15, further comprising at least one ripcord between saidplurality of flextubes and said sheath.
 20. The optical cable accordingto claim 15, further comprising strength members in said sheath.